The invention relates generally to the field of differential fluid pressure measuring apparatus and flowmeters. Monitoring the rate at which fluid is flowing in a line is frequently necessary, particularly where the rate of flow has to be controlled within certain limits in process applications requiring a supply of one fluid component at a nominal rate, or where the rate of flow is indicative of a system input requiring adjustment of system variables, such as in chemical refineries. An instrument which has proved effective and versatile for measuring flow rate is the direct reading vane-type flowmeter shown for example in U.S. Pat. Nos. 2,873,606, 2,892,348 and 3,090,231 to Regner A. Ekstrom, Jr.
With advances in process control technology and the growth of more sophisticated and demanding applications over the years, it has become desirable in many situations to have a remote electrical readout indicative of flow rate in a particular fluid line, for example, in a Petroleum plant. The science of transduction has in the meantime developed several ways to convert flow rate to an electrical signal, for example, turbines with rotating magnets and acoustical Doppler effect devices. These systems, while producing electrical outputs, require relatively complicated circuitry and either suffer poor reliability in demanding applications or are extremely expensive. Another type of flowmeter with an electrical output employs a strain gauge mounted on an arm projecting into the line, which is deflected by the force of the impinging stream.
While these systems have their place, there remains an unfilled need for a low-cost, rugged, versatile instrument for monitoring flow rate particularly in the types of environments and applications served by vane-type and other differential pressure type flowmeters in the past.